Active immunisation against influenza virus has been performed for many years. As of 2010 this involves seasonal production of trivalent vaccines which are then administered to at-risk populations, usually before winter begins. Current vaccines are mainly based on inactivated viruses, with dosing being based on their amount of viral hemagglutinin, but there is also one live attenuated vaccine.
In addition to seasonal trivalent vaccines the 2009 “swine flu” H1N1 pandemic led to widespread use of a monovalent vaccine.
All but one of the current seasonal vaccines licensed in the developed world are unadjuvanted. The exception is the FLUAD™ product which is adjuvanted with a squalene-in-water emulsion called MF59™. Oil-in-water emulsion adjuvants were also included in several monovalent H1N1 pandemic vaccines such as FOCETRIA™ and CELTURA™ (both with MF59™ adjuvant), AREPANRIX and PANDEMRIX (both with AS03 adjuvant), and HUMENZA (with AF03 adjuvant). The aim of including adjuvants in these vaccines is to improve the immune response which is mounted against the viral antigens.
Inclusion of an adjuvant can increase the quality and/or quantity of a recipient's immune response against influenza vaccines. A large number of clinical trials with MF59™-adjuvanted influenza vaccines have confirmed that the adjuvant provides higher immunogenicity and also protects better against infection with heterovariant potentially mismatched strains [1], but these effects have not been shown in epidemiological studies to avert cases of influenza or to reduce related complications.